JP2952978B2 - Transparent yttria sintered body and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention has both excellent translucency and mechanical strength,
In particular, the present invention relates to a translucent yttria sintered body suitable for use as an infrared transmission window having a thickness of 3 mm or more, and a method for producing the same.

[Conventional technology]

It is known that yttria (Y ₂ O ₃ ) has a cubic crystal form at 2350 ° C or less, so it has little scattering at the crystal grain boundaries and exhibits very high light transmittance when sintered at high density. .

Normally, the light transmittance of the yttria sintered body is 0.
It rises sharply from around 3 μm and has a wavelength of 3 to 6 in the infrared region.
It is highest near μm. Therefore, the yttria sintered body is regarded as promising as a translucent material such as an optical window, and its production has been attempted by various methods.

For example, as described in JP-A-54-17911 and JP-A-54-17910, lanthanum oxide (La ₂ O ₃ ) or alumina (Al ₂ O ₃ ) is added as a sintering aid. There is a method of sintering in a low O ₃ atmosphere.However, in the method using this sintering aid, although the densification is easy and the mechanical strength is high, the sintering aid remains in the sintered body. Therefore, there is a disadvantage that light is scattered due to systematic inhomogeneity and the transmittance is reduced, and therefore, a large material having a diameter of 50 mm or more is optically uniform. It was difficult to obtain the material. Also, when La ₂ O ₃ etc. is added, the thermal conductivity becomes 7 W / m
-There is a disadvantage that the temperature decreases to about K and the thermal shock resistance also decreases.

U.S. Pat. No. 3,878,280 discloses a method of hot pressing yttria powder in a vacuum. But,
With this method, 500kg /
It is difficult to apply a high pressure of ² cm ² or more, so that sufficient densification does not proceed and the transmittance is low.

Further, as disclosed in JP-A-63-201061, Y ₂ O ₃
After pressureless sintering the powder at 1700-1900 ° C to make closed pores,
A method of performing HIP processing at a pressure of 25000 to 30000 psi and a temperature of 1700 to 1900 ° C. is also known. However, in this method, since both the sintering temperature and the HIP temperature are higher than 1700 ° C., the average crystal grain size of the Y ₂ O ₃ sintered body is as coarse as about 150 μm, and the bending strength is 1
There was a drawback that sufficient thermal shock resistance could not be obtained because the residual strain remained at about 10 MPa and many residual strains were generated.

Therefore, in the yttria sintered body manufactured by each of the conventional methods described above, the wavelength is 3 to 6 μm at a sample thickness of 2.5 mm.
Infrared transmission window used with a thickness of 3 mm or more, since the maximum linear transmittance at about 80% is about 80%, and the higher the linear transmittance, the lower the bending strength and the more the occurrence of residual strain. In order to use these materials, it is necessary to simultaneously improve the linear transmittance and the bending strength and reduce the residual strain.

[Problems to be solved by the invention]

In view of such conventional circumstances, the present invention has excellent translucency with high purity and high strength at the same time, and particularly has a linear transmittance suitable as an infrared transmitting window material having a thickness of 3 mm or more, An object of the present invention is to provide a translucent yttria sintered body that is optically uniform even with a large material and has no crack or residual strain, and a method for producing the same.

[Means for solving the problem]

In order to achieve the above object, in the method for producing a translucent yttria sintered body of the present invention, an yttria powder having a purity of 99.9% or more and a specific surface area (BET value) of 2 m ² / g or more and less than 10 m ² / g is subjected to temperature 1300-1700 densified to 95% or more theoretical density ratio by Hotsutopuresu in a vacuum at ° C. and a pressure 100 to 500 kg / cm ^2, to HIP treatment then at a temperature from 1,400 to 1,900 ° C. and a pressure of 500 kg / cm ² or more Features.

The translucent yttria sintered body produced by the above method is composed of a polycrystalline yttria sintered body having a purity of 99.9% or more and has a linear transmittance at a sample thickness of 3 mm in the infrared region having a wavelength of 3 to 6 μm. % Or more, the average crystal grain size is 100 μm or less, and the four-point bending strength is 120 MPa or more.

[Action]

In the method of the present invention, hot press in vacuum and subsequent HIP (hot isostatic press) are performed without using a sintering aid, and the linear transmittance is spatially uniform and high, and at the same time, it is excellent in bending strength. A sintered body can be obtained.

The yttria powder, which is a raw material of the sintered body, has a purity of 99.9% or more in order to prevent a decrease in translucency due to absorption of impurities, and particularly contains no transition metal element such as Fe.

In addition, the yttria powder has a primary particle size of about 0.4 to 0.2 μm.
m, that is, the surface area needs to be ² m ² / g or more and less than 10 m ² / g in BET value. A powder having a BET value of 10 m ² / g or more is not suitable as a precision optical component because cracks are likely to occur in a hot press due to bridging of particles and even if cracks do not occur, excessive strain remains. On the other hand, if it is less than 2 m ² / g, it is difficult to increase the density during hot pressing, and the densification by HIP becomes insufficient, and the transmittance decreases. That is, the surface area of the yttria powder is 2m ² / g in BET value.
When it is less than 10 m ² / g, one of the conditions necessary for obtaining a dense sintered body which is excellent in light transmittance, free of residual strain and cracks, and has a fine crystal grain size.

Furthermore, since a sintering aid such as La ₂ O _{3 is} not added, the transmittance, the spatial nonuniformity, and the thermal conductivity due to the second phase do not occur.

In the hot pressing step of the method of the present invention, the temperature was raised to 1300
It is difficult to obtain a high-density sintered body with a theoretical density ratio of 95% or more when the temperature is lower than 1300 ° C, and when the temperature exceeds 1700 ° C, oxygen ions in Y ₂ O ₃ are removed from the surface in a vacuum. The reason for this is that the composition ratio deviates and the composition ratio shifts, making it difficult to obtain an optically uniform sintered body. If the pressure is less than 100 kg / cm ^2, it is still difficult to obtain a high-density sintered body having a theoretical density ratio of 95% or more, and if it exceeds 500 kg / cm ² , it becomes difficult to use a graphite type in terms of strength. When the theoretical density ratio of the sintered body obtained by the hot press is less than 95%, most of the residual pores become so-called open pores, and high-pressure gas enters the interior through the pores in the subsequent HIP treatment, This is because the HIP treatment does not sufficiently increase the density.

In the HIP step, the temperature is set to 1400 to 1900 ° C. (preferably 1400 to 1700 ° C.). If the temperature is lower than 1400 ° C., the effect of removing pores becomes insufficient and satisfactory light transmittance cannot be obtained.
If the temperature exceeds 1900 ° C., the grain growth becomes extremely coarse and sufficient bending strength cannot be obtained. HIP pressure 500kg / c
If the pore size is less than m ² , the pores are not sufficiently removed and satisfactory translucency cannot be obtained. However, the upper limit of the pressure is usually about 2000 kg / cm ² due to the limited capacity of the HIP device. The gas used in the HIP treatment is preferably an inert gas such as Ar, a nitrogen gas or an oxygen gas, or a mixed gas thereof. In particular, by mixing an oxygen gas, the translucent property by deoxygenation from the sintered body is obtained. There is an advantage that a decrease in the temperature can be prevented.

As described above, in the method of the present invention, the hot press temperature is 1300
Since the process at 1700 ° C. and the HIP temperature at 1400 ° C. to 1900 ° C. can be clearly performed at a lower temperature than the conventional method, crystal grain growth is suppressed and a fine and high-strength sintered body can be obtained. That is, the average crystal grain size of the obtained yttria sintered body is in the range of 2 to 100 μm, which is finer than the conventional one, and the four-point bending strength is also 120.
It is higher than MPa but as high as 180 MPa at the maximum, and the thermal shock resistance, which is an important property as an infrared transmission window material, is remarkably improved and improved as compared with the conventional one.

〔Example〕

Example 1 High purity Y ₂ O ₃ having a purity of 99.9% and a specific surface area of 4.6 m ² / g (BET value)
The powder was 3 × 10 ^-3 t using a graphite mold with an inner diameter of 120 mm.
3 at a temperature of 1450 ° C and a pressure of 300 kg / cm ² in a vacuum of orr
Hot pressing was performed for a time to obtain a white sintered body having a theoretical density ratio of 98%. Next, this sintered body was put into a HIP apparatus, and HIP treatment was performed for 2 hours at a temperature of 1620 ° C. and a pressure of 2000 kg / cm ² using Ar gas. The obtained Y ₂ O ₃ sintered body was colorless and transparent in appearance.

The obtained Y ₂ O ₃ sintered body was mirror-polished to a thickness of 3 mm, and the linear transmittance was measured with a spectrophotometer.
m showed a translucency of 82% or more in the infrared region. When the strain was measured with a photoelastic device, no interference fringes due to residual strain were observed. The average crystal grain size of this sintered body is 25 μm,
The four-point bending strength based on JIS R 1601 was 156 MPa.

Example 2 High purity Y ₂ O ₃ having a purity of 99.9% and a specific surface area of 3.5 m ² / g (BET value)
The powder was 3 × 10 ^-3 t using a graphite mold with an inner diameter of 120 mm.
3 at a temperature of 1650 ° C and a pressure of 150 kg / cm ² in a vacuum of orr
Hot pressing was performed for a time to obtain a white sintered body having a theoretical density ratio of 97%. Next, this sintered body was placed in a HIP apparatus, and HIP treatment was performed for 1 hour at a temperature of 1750 ° C. and a pressure of 2000 kg / cm ² using Ar gas. The obtained Y ₂ O ₃ sintered body was colorless and transparent in appearance.

The obtained Y ₂ O ₃ sintered body was mirror-polished to a thickness of 3 mm, and the linear transmittance was measured with a spectrophotometer.
m showed a translucency of 81% or more in the infrared region. When the strain was measured with a photoelastic device, no interference fringes due to residual strain were observed. The average crystal grain size of this sintered body is 90 μm,
The four-point bending strength based on JIS R 1601 was 124 MPa.

Example 3 High purity Y ₂ O ₃ having a purity of 99.9% and a specific surface area of 8.5 m ² / g (BET value)
The powder was 3 × 10 ^-3 t using a graphite mold with an inner diameter of 120 mm.
5 at 1320 ° C and 450 kg / cm ² in orr vacuum
Hot pressing was performed for a time to obtain a white sintered body having a theoretical density ratio of 98%. Next, this sintered body was put into a HIP apparatus, and HIP treatment was performed for 2 hours at a temperature of 1600 ° C. and a pressure of 2000 kg / cm ² using Ar gas. The obtained Y ₂ O ₃ sintered body was colorless and transparent in appearance.

The obtained Y ₂ O ₃ sintered body was mirror-polished to a thickness of 3 mm, and the linear transmittance was measured with a spectrophotometer.
m showed a light transmittance of 80% or more in the infrared region. When the strain was measured with a photoelastic device, no interference fringes due to residual strain were observed. The average crystal grain size of this sintered body is 2 μm,
The four-point bending strength based on JIS R 1601 was 172 MPa.

Example 4 In the same manner as in Example 1, a white sintered body having a theoretical density ratio of 98% was obtained. This sintered body was put in an HIP apparatus, N ₂ gas line the HIP treatment for 2 hours at a temperature 1600 ° C. and a pressure of 2000 kg / cm ² using a Natsuta, Y ₂ O ₃ sintered body obtained is aesthetically It was colorless and transparent.

The same measurement as in Example 1 was performed on the obtained Y ₂ O ₃ sintered body. As a result, the linear transmittance at a wavelength of 3 to 6 μm with a sample thickness of 3 mm was 81% or more, and interference fringes due to residual strain were observed. Is not observed, and the average crystal grain size of the sintered body is
The four-point bending strength based on R 1601 was 160 MPa.

Example 5 In the same manner as in Example 3, a white sintered body having a theoretical density ratio of 98% was obtained. This sintered body was put into a HIP apparatus, and HIP was performed at a temperature of 1500 ° C. and a pressure of 2000 kg / cm ² for 4 hours using Ar-4% O ₂ gas.
Processing was performed. The obtained Y ₂ O ₃ sintered body was colorless and transparent in appearance.

The same measurement as in Example 1 was performed on the obtained Y ₂ O ₃ sintered body. As a result, the linear transmittance at a wavelength of 3 to 6 μm with a sample thickness of 3 mm was 80% or more, and interference fringes due to residual strain were observed. Is not observed, and the average crystal grain size of the sintered body is
The four-point bending strength based on R 1601 was 162 MPa.

Comparative Example High purity Y ₂ O _{3 with} 99.9% purity and specific surface area of 19.6 m ² / g (BET value)
The powder was 3 × 10 ^-3 t using a graphite mold with an inner diameter of 120 mm.
3 at a temperature of 1350 ° C and a pressure of 250 kg / cm ² in a vacuum of orr
Hot pressing was performed for a time to obtain a white sintered body having a theoretical density ratio of 98%. This sintered body was placed in a HIP device, and a temperature of 1650 ° C. and a pressure of 2000 kg / cm ² were used using Ar gas.
HIP treatment for 2 hours. The obtained Y ₂ O ₃ sintered body was colorless and transparent in appearance.

The same measurement as in Example 1 was performed on the obtained Y ₂ O ₃ sintered body, and as a result, the linear transmittance at a wavelength of 3 to 6 μm with a sample thickness of 3 mm was 81% or more, but due to residual strain. Interference fringes were observed. The average grain size of the sintered body is 20 μm.
The four-point bending strength based on JIS R 1601 was 160 MPa.

〔The invention's effect〕

According to the present invention, without using a sintering aid, it has a fine crystal grain size and high strength, and simultaneously has a wavelength of 3 to 6 μm.
Excellent linear transmittance in the infrared region, thickness of 50 mm or more
Even with a large material of 3 mm or more, it is possible to obtain a translucent yttria sintered body that is optically uniform and free from equality and distortion.

This translucent yttria sintered body is particularly useful as an infrared transmission window material having a thickness of 3 mm or more.

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Claims (3)

(57) [Claims] (1) a purity of 99.9% or more and a specific surface area (BET value) of 2 m ^2;
/ g or more and less than 10 m ² / g yttria powder, temperature 1300-1700
Densification to a theoretical density ratio of 95% or more by hot pressing in vacuum at 100 ° C. and a pressure of 100 to 500 kg / cm ^2.
A method for producing a translucent yttria sintered body, characterized by performing HIP treatment at 00 to 1900 ° C. and a pressure of 500 kg / cm ² or more. 2. The method for producing a translucent yttria sintered body according to claim 1, wherein the HIP treatment uses an inert gas, a nitrogen gas, an oxygen gas, or a mixed gas thereof. 3. A sintered body made of polycrystalline yttria having a purity of 99.9% or more, and a linear transmittance at a sample thickness of 3 mm having a wavelength of 3 to 6 μm.
m is at least 80% in the infrared region, and the average crystal grain size is 100μ.
m, and a four-point bending strength of 120 MPa or more.